Light metal piston



y 19320 L. KRAEMER I LIGHT METAL PISTQN Filed May 26, 1930 Patented July 19, 1932 PATENT OFFICE LUDWIG KRAEMER, OF COLOGNE-mNSFELD, GERMANY LIGHT METAL PISTON Application filed Kay 28, 1930,5erla1 No. 455,761,and in Germany November 10, 1828.

Internal combustion engines of all kinds were until recently made with gray cast iron pistons, or with pistons of the material used or making the cylinders. On account of the 5 increase in compression, and the constantly rising speed of revolution, it became necessary to seek other materials from which pistons could be made. Besides aluminium, electron was favoured on account of its small specific gravity and high thermal conductivity.

All light metal pistons, however, have the disadvantage that, when heated, they expand considerably more than the castiron cylinders in which they move. In consequence of this, these light metal pistons must be built in with much greater clearance (twice as great as with cast iron pistons), in spite of the fact that they lead away the heat much more quickly than cast iron pistons-the former scarcely reach a maximum temperature of 250, while the latter under the same conditions reach 400500. When cold, a machine provided with light metal pistons is therefore inclined to rattle. -Moreover, the

life of light metal pistons is always comparatively short, since with normal wear, the piston soon reaches the limit where it can no longer provide sufiicient filling in the cold state. Attempts have been made to overcome this disadvantage by using two different metals for making the pistons. In these pistons the dissipation of heat is improved, but the life is no longer than that of previously known light metal pistons.

It has now been found possible to construct a light metal piston which has a dissipation of heat so favorable that the piston can be built in with the same small clearance as a cast iron piston, and, which moreover has a life equal to that of the cast iron piston.

The invention consists in this, that the heat produced at the top of the piston is led away directly to the side of the cold cylinder wall through a thickening of the material at a well defined part of the piston, namely where, at the moment of the explosion, that is at the time of the greatest lateral pressure the piston lies closely against the cylinder wall. At the same time, in order further to diminish the conduction of heat to the shank, the gudgeon pin bearings are preferably separated from the shank, and connected to the top part of the piston by several strong ribs,

' and, moreover, slots are provided in the shank of the piston, and the top of the piston and the shank are partly separated by slots.

Figure 1 isa longitudinal sectional view through the piston taken on a line at right angles to the gudgeon pin bearings:

Figure 2 is an elevatlonal view of the interior of a modified form of piston;

Figure 3 is a transverse sectional view taken on the line III-III of Figure 1;

Figure 4 is a transverse sectional view taken on' the line IVIV of Figure 2 clearly illustrating the use of a pair of bridges for bracing the piston shank; and

Figure 5 is a transverse sectional view taken on the line VV of Figure 1, illustrating an arrangement of bridges which pro duces a more rigid shank than that shown in Figures 2-and 4.

lVhen the top of the piston 2, (Figures 1 and 2) becomes heated while the motor is running, the heat is carried awa through the thickening of the material 1, igures land 3) by the cooled cylinder wall, immediately after the explosion at the moment when the side 6 of the shank lies closely against the cylinder wall, in an amount and with a speed such as is possible at no other part of the running motor. A small part of the heat goes through the ribs 4, (Fi ures 1 and 3) to the gudgeon pin bearing 3, igures 1 and 2), and from here to the connecting rod,'since the bearings are separated from the shank. To prevent the spreading of heat in the shank 5 and 6 of'the piston, (Figure 1), one or more slots 9, (Figures 2, 4 and 5) are provided opposite the thickening of the material 1, (Figures 1 and 3), or to the right and left of it. The greater part of the heat can therefore only take the desired path to the wall of the cylinder. In order to prevent direct radiation from the top of the piston 2 to the shank 5 and 6, (Figure 1), the shank is separated as at 8, (Figure 2) from the top of the piston, either only at one side or up to the thickening of the material 1, (Figures 1 and 3).

In order to fit the open end of the piston in the cylinder with the smallest possibleclearance under all operating conditions, in spite of the fact that a heating of the open end of the piston takes place, either through direct conduction or by radiation of heat,

two straight flat bridges 10, (Figure 4) are built in, below the gudgeon pin, across the piston axis, that is perpendicular .to the direction of pressure, which may have any de- V sired shape, but are preferably about 1 cm." high and about cm. broad. As these bridges are connected with the shank through only a small cross-section at each end, the heat led to the piston shank from the top of the piston is only transferred to these bridges.

to a limited extent. Further,'the bridges are strongly cooled'by the oil thrown upwards by the crank shaft and connecting rod, so. that the temperature difference between bridge and shank is again considerably increased. Consequently these bridges expand less, and for this reason hold the piston together in the perpendicular direction of the bridges, that is, the piston cannot expand as much as it would in the absence of the bridges. Accordingly, it is not necessary, as hitherto with light metal pistons, to give the piston a large clearance in order'to avoid seizing, but the piston may at its open end be fitted closely in the cylinder boring, without any fear of its running tight. At the same time it is achieved that on account of the close fit of the end of the piston, the lower edge of the piston scrapes the .oil, which is thrown' upwards cleanly from the cylinder wall, and

the undesirable pump action, which pistons with large clearance produce, does not occur. Moreover, the piston is stayed in the direction of pressure by these bridges, without the elasticity of the slotted piston being in any way detrimentally affected. The unpleasant noise produced by hitherto used slotted pistons, which results in a loud operation of the motor, is avoided, and the motor runs quiet- Iy, easily and elastically. For constructional reasonsand for reasons based on the technique of casting, the bridge may be placed directly below the gudgeon pin bearing, or at a greater distance from it. In the latter case lateral slots are employed for introducing the casting tool of the piston shank.

For special purposes it is necessary to stay the, piston with more than two bridges, e. g.

with other similar bridgesalso' parallel to of the great expansion at raisedtem'peratures and the excess ofoil about the piston connected therewith. By means of the above described apparatus, it is for the first time possible for the end of the piston always to fit closely against the cylinder wall under operating conditions, and thereby effectively to oppose the accumulationof oil aboutthe piston even without the use of piston rings. For with too great clearance at the end of the piston a pumpv action arises which continuously feeds the oil to the rings, and often in such amounts that the most different constructions of piston rings cannot hold this oil back. The resultis that the cylinder and the sparking plug are choked up with oil.

Finally, it has now been found that the slot which divides the piston into two parts between the gudgeon pin bearing and the top of the piston, and of which the length is limited by the breadth of the window over the gudgeon pin, may be extended, and the transfer of heat from the top of the piston to the shank of the piston may be effectively prevented, by projections 7 cast on the inside of the piston in the plane of this' slot, which connect the separated parts of the shank. It 'is thereby possible to carry through the slot into a section, so that a very considerable extension of the slot, and also a great stiffening is obtained. The projection is divided by the slot itself and the lower bridge of the projection lies in the direction of the oil, which is thrown upwards, like the previously described bridges on the shank of the piston. There is thus also a temperature difference between the two sides of the projection; the lower part of the projection remains cooler, expands less, and restrains the increase in diameter of the whole shank of the piston with the result that the clearance with which the piston is built in can be still further diminished.

What. I claim is:

A piston of light metal having its wall, on the side thereof which bearsv against the cylinder under the lateral thrust produced by the obliquity of the connecting rod, thickened so as to form a mass of material exceeding that required for stiffening the wall of spread of heat from the thickened portion of the piston .wall, a slot between the top of the piston and the lower part of the piston on the side thereof remote from the thickened portion of the piston wall and bridges below the gudgeon pin extending transverse- 1y to the axis of the piston, connected to the wall of'the piston only at their ends and having a smell cross section at their ends for minimizing the transfer of heat from the wall of the piston to the bridges.

In testimony whereof I have signed my name to this specification.

LUDWIG KRAEMER. 

